arXiv subjects

M. López de Haro

Publications and source records attributed to M. López de Haro.

14 recordsLinked to original sources

arXiv2021

Internal structure and heat conduction in rigid solids: a two temperature approach

A non-Fourier thermal transport regime characterizes the heat conduction in solids with internal structure. Several thermodynamic theories attempt to explain the separation from the Fourier regime in such kind of systems. Here we develop a two temperature model to describe the non-Fourier regime from the principles of non-equilibrium thermodynamics. The basic assumption is the existence of two well separated length scales in the system, namely, one related with the matrix dimension (bulk) and the other with the characteristic length of the internal structure. Two Fourier type coupled transport equations are obtained for the temperatures which describe the heat conduction in each of the length scales. Recent experimental results from several groups on the thermal response of different structured materials are satisfactorily reproduced by using the coupling parameter as a fitting parameter. The similarities and differences of the present formalism with other theories are discussed.

physics.class-ph↗

arXiv2020

Structural properties of additive binary hard-sphere mixtures

An approach to obtain the structural properties of additive binary hard-sphere mixtures is presented. Such an approach, which is a nontrivial generalization of the one recently used for monocomponent hard-sphere fluids [S. Pieprzyk, A. C. Brańka, and D. M. Heyes, Phys. Rev. E 95, 062104 (2017)], combines accurate molecular-dynamics simulation data, the pole structure representation of the total correlation functions, and the Ornstein-Zernike equation. A comparison of the direct correlation functions obtained with the present scheme with those derived from theoretical results stemming from the Percus-Yevick (PY) closure and the so-called rational-function approximation (RFA) is performed. The density dependence of the leading poles of the Fourier transforms of the total correlation functions and the decay of the pair correlation functions of the mixtures are also addressed and compared to the predictions of the two theoretical approximations. A very good overall agreement between the results of the present scheme and those of the RFA is found, thus suggesting that the latter (which is an improvement over the PY approximation) can safely be used to predict reasonably well the long-range behavior, including the structural crossover, of the correlation functions of additive binary hard-sphere mixtures.

cond-mat.soft↗

arXiv2016

Theoretical approaches to the structural properties of the square-shoulder fluid

A comparison of simulation results with the prediction of the structural properties of square-shoulder fluids is carried out to assess the performance of three theories: Tang--Lu's first-order mean spherical approximation, the simplified exponential approximation of the latter and the rational-function approximation. These three theoretical developments share the characteristic of being analytical in Laplace space and of reducing in the proper limit to the Percus--Yevick result for the hard-sphere fluid. Overall, the best agreement with the simulation data is obtained with the simplified exponential approximation.

cond-mat.soft↗

arXiv2015

Equation of state and critical point behavior of hard-core double-Yukawa fluids

A theoretical study on the equation of state and the critical point behavior of hard-core double-Yukawa fluids is presented. Thermodynamic perturbation theory, restricted to first order in the inverse temperature and having the hard-sphere fluid as the reference system, is used to derive a relatively simple analytical equation of state of hard-core multi-Yukawa fluids. Using such an equation of state, the compressibility factor and phase behavior of six representative hard-core double-Yukawa fluids is examined and compared with available simulation results. The effect of varying the parameters of the hard-core double-Yukawa intermolecular potential on the location of the critical point is also analyzed using different perspectives. The relevance of this analysis for fluids whose molecules interact with realistic potentials is also pointed out.

cond-mat.stat-mech↗

arXiv2012

Rational-function approximation for fluids interacting via piece-wise constant potentials

The structural properties of fluids whose molecules interact via potentials with a hard-core plus n piece-wise constant sections of different widths and heights are derived using a (semi-analytical) rational-function approximation method. The results are illustrated for the cases of a square-shoulder plus square-well potential and a shifted square-well potential and compared both with simulation data and with those that follow from the (numerical) solutions of the Percus-Yevick integral equation.

cond-mat.soft↗

arXiv2011

Use of the attractive hard-core Yukawa interaction for the derivation of the phase diagram of liquid water

The phase diagram of the attractive hard-core Yukawa fluid derived previously [M. Robles and M. López de Haro, J. Phys. Chem. C 111, 15957 (2007)] is used to obtain the liquid-vapor coexistence curve of real water. To this end, the value of the inverse range parameter of the intermolecular potential in the Yukawa fluid is fixed so that the ratio of the density at the critical point to the liquid density at the triple point in this model coincides with the same ratio in water. Subsequently, a (relatively simple) nonlinear rescaling of the temperature is performed which allows one to obtain the full liquid vapor coexistence curve of real water in the temperature-density plane with good accuracy, except close to the triple point. Such rescaling may be physically interpreted in terms of an effective temperature-dependent attractive hard-core Yukawa interaction potential which in turn introduces an extra temperature dependence in the equation of state. With the addi- tion of a multiplicative factor to obtain from the model the critical pressure of real water, the corrected equation of state yields reasonably accurate isotherms in the liquid phase region except in the vicinity of the critical isotherm and in the vicinity of the triple point isotherm. The liquid-vapor coexistence curves in the pressure-temperature and pressure-density planes are also computed and a possible way to improve the quantitative agreement with the real data is pointed out.

cond-mat.stat-mech↗

arXiv2011

Structure of the square-shoulder fluid

The structural properties of square-shoulder fluids are derived from the use of the rational function approximation method. The computation of both the radial distribution function and the static structure factor involves mostly analytical steps, requiring only the numerical solution of a single transcendental equation. The comparison with available simulation data and with numerical solutions of the Percus-Yevick and hypernetted-chain integral equations shows that the present approximation represents an improvement over the Percus-Yevick theory for this system and a reasonable compromise between accuracy and simplicity.

cond-mat.stat-mech↗

arXiv2009

Contact values for disparate-size hard-sphere mixtures

A universality ansatz for the contact values of a multicomponent mixture of additive hard spheres is used to propose new formulae for the case of disparate-size binary mixtures. A comparison with simulation data and with a recent proposal by Alawneh and Henderson for binary mixtures shows reasonably good agreement with the predictions for the contact values of the large-large radial distribution functions. A discussion on the usefulness and limitations of the new proposals is also presented.

cond-mat.soft↗

arXiv2008

Simple equation of state for hard disks on the hyperbolic plane

A simple equation of state for hard disks on the hyperbolic plane is proposed. It yields the exact second virial coefficient and contains a pole at the highest possible packing. A comparison with another very recent theoretical proposal and simulation data is presented.

cond-mat.soft↗

arXiv2002

On the liquid-glass transition line in monatomic Lennard-Jones fluids

A thermodynamic approach to derive the liquid-glass transition line in the reduced temperature vs reduced density plane for a monatomic Lennard-Jones fluid is presented. The approach makes use of a recent reformulation of the classical perturbation theory of liquids [M. Robles and M. López de Haro, Phys. Chem. Chem. Phys. {\bf 3}, 5528 (2001)] which is at grips with a rational function approximation for the Laplace transform of the radial distribution function of the hard-sphere fluid. The only input required is an equation of state for the hard-sphere system. Within the Mansoori-Canfield/Rasaiah-Stell variational perturbation theory, two choices for such an equation of state, leading to a glass transition for the hard-sphere fluid, are considered. Good agreement with the liquid-glass transition line derived from recent molecular dynamic simulations [Di Leonardo et al., Phys. Rev. Lett. {\bf 84}, 6054(2000)] is obtained.

cond-mat.stat-mech↗

arXiv2001

Virial coefficients and equations of state for mixtures of hard discs, hard spheres and hard hyperspheres

The composition-independent virial coefficients of a $d$-dimensional binary mixture of (additive) hard hyperspheres following from a recent proposal for the equation of state of the mixture [Santos, A., Yuste, S. B., and López de Haro, M., 1999, Molec. Phys., 96, 1] are examined. Good agreement between theoretical estimates and available exact or numerical results is found for $d=2$, 3, 4 and 5, except for mixtures whose components are very disparate in size. A slight modification that remedies this deficiency is introduced and the resummation of the associated virial series is carried out, leading to a new proposal for the equation of state. The case of binary hard-sphere mixtures ($d=3$) is analyzed in some detail.

cond-mat.stat-mech↗

arXiv2001

Comment on "Theory and computer simulation for the equation of state of additive hard-disk fluid mixtures"

A flaw in the comparison between two different theoretical equations of state for a binary mixture of additive hard disks and Monte Carlo results, as recently reported in C. Barrio and J. R. Solana, Phys. Rev. E 63, 011201 (2001), is pointed out. It is found that both proposals, which require the equation of state of the single component system as input, lead to comparable accuracy but the one advocated by us [A. Santos, S. B. Yuste, and M. López de Haro, Mol. Phys. 96, 1 (1999)] is simpler and complies with the exact limit in which the small disks are point particles.

cond-mat.stat-mech↗

arXiv2000

Demixing in binary mixtures of hard hyperspheres

The phase behavior of binary fluid mixtures of hard hyperspheres in four and five dimensions is investigated. Spinodal instability is found by using a recent and accurate prescription for the equation of state of the mixture that requires the equation of state of the single component fluid as input. The role played by the dimensionality on the possible metastability of the demixing transition with respect to a fluid-solid transition is discussed. The binodal curves in the pressure--chemical potential representation are seen to lie on a common line, independent of the size ratio

cond-mat.stat-mech↗

arXiv2000

Direct correlation functions and bridge functions in additive hard-sphere mixtures

A method to obtain (approximate) analytical expressions for the radial distribution functions in a multicomponent mixture of additive hard spheres that was recently introduced is used to obtain the direct correlation functions and bridge functions in these systems. This method, which yields results practically equivalent to the Generalized Mean Spherical Approximation and includes thermodynamic consistency, is an alternative to the usual integral equation approaches and requires as input only the contact values of the radial distribution functions and the isothermal compressibility. Calculations of the bridge functions for a binary mixture using the Boubl\'ık-Mansoori-Carnahan-Starling-Leland equation of state are compared to parallel results obtained from the solution of the Percus-Yevick equation. We find that the conjecture recently proposed by Guzmán and del R\'ıo (1998, {\em Molec. Phys.}, {\bf 95}, 645) stating that the zeros of the bridge functions occur approximately at the same value of the shifted distance for all pairs of interactions is at odds with our results. Moreover, in the case of disparate sizes, even the Percus-Yevick bridge functions do not have this property. It is also found that the bridge functions are not necessarily non-positive.

cond-mat.stat-mech↗